What every operator should know about sanitary sewer overflows

An SSO
is any overflow, spill, release, discharge, or diversion of untreated or
partially treated wastewater from a sanitary sewer system. SSOs often contain
high levels of suspended solids, pathogenic organisms, toxic pollutants,
nutrients, oil, and grease. SSOs pollute surface waters and groundwaters,
threaten public health, adversely affect aquatic life, and impair the
recreational use and aesthetic enjoyment of surface waters. Typical
consequences of SSOs include closures of beaches and other recreational
areas, inundated properties, and polluted rivers and streams.

Check
with your state’s environmental protection agency or water resource board for
any updated requirements.

Reporting/documentation

Take
pictures and compile an SSO report that includes a clear chronology and
description of events and actions taken.

This
report is incorporated into the SSO event record for data capture and trend
tracking. The report also should include a spill-volume estimation worksheet
and any service requests or other field documentation.

Ensure
that all required documentation forms are available on all response vehicles.

SSO
estimation — measured volume method

The
volume of many small SSOs that have been contained can be estimated using
this method. The shape, dimensions, and depth of the contained wastewater are
needed. The shape and dimensions are used to calculate the area of the SSO,
and the depth is used to calculate volume.

Use
geometric shapes (e.g., rectangles, circles, triangles, etc.) when
determining the size of the spill.

SSO
estimation — duration and flow rate method

Calculating the volume of larger SSOs, where it is
difficult or impossible to measure the area and depth of the collected water,
requires a different approach. In this method, separate estimates are made of
the duration of the SSO and the flow rate. This method can be used only when
an overflow is observed in progress.

Agencies
should develop handouts that show pictures of how different flow rates look
pouring from the style of manhole lids in use in the area.

SSO
estimation — eyeball method

To use
this method, imagine the amount of water that would spill from a jug, bucket,
or barrel. A jug contains 3.8 L (1 gal), a bucket contains 19 L (5 gal), and
a barrel contains 209 L (55 gal).

If the SSO is larger than 209 L (55 gal), try to break
the standing water into barrels and then multiply by 209 L (55 gal). This
method is useful for contained SSOs up to approximately 760 L (200 gal).

Agencies
should train employees on the visual difference in spills ranging between 3.8
and 209 L (1 and 55 gal).

Secure
SSOs from the public

To
secure an SSO area, install barricades, cones, or lighted barricades to keep
the public out of the area.

If the
SSO enters surface waters, signs may have to be posted prohibiting the public
from water contact.

Cordon-off
the area with caution tape.

Advise
any unauthorized people to shower or seek medical attention if they were
exposed to any significant amount of wastewater.

Containment

Containing
an SSO may include but is not limited to the following actions:

 Plug any catch-basin outlets, or use
rubber mats to cover
the catch-basin inlet.